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Open your developer tools and enter the following command in the Console:

window.adobeDataLayer.getState();

To see the current state of the data layer on an AEM site inspect the response. You should see information about the page and individual components.

Push a data object on to the data layer by entering the following in the console:

window.adobeDataLayer.push({
    "component": {
        "training-data": {
            "title": "Learn More",
            "link": "learn-more.html"
        }
    }
});

Run the command adobeDataLayer.getState() again and find the entry for training-data.

Next add a path parameter to return just the specific state of a component:

window.adobeDataLayer.getState('component.training-data');

Enter the following helper method in your console:

function getDataObjectHelper(event, filter) {
    if (event.hasOwnProperty("eventInfo") && event.eventInfo.hasOwnProperty("path")) {
        var dataObject = window.adobeDataLayer.getState(event.eventInfo.path);
        if (dataObject != null) {
            for (var property in filter) {
                if (!dataObject.hasOwnProperty(property) || (filter[property] !== null && filter[property] !== dataObject[property])) {
                    return;
                }
                return dataObject;
            }
        }
    }
    return;
}

The above code inspects the event object and uses the adobeDataLayer.getState method to get the current state of the object that triggered the event. Then helper method inspects the filter and only if the current dataObject meets the filter criteria it is returned.

Next, enter an event handler that is called when a Teaser component is shown within a Carousel.

function teaserShownHandler(event) {
    var dataObject = getDataObjectHelper(event, {"@type": "wknd/components/carousel/item"});
    if(dataObject != null) {
        console.log("Teaser Shown: " + dataObject['dc:title']);
        console.log(dataObject);
    }
}

The teaserShownHandler function calls the getDataObjectHelper function and passes a filter of wknd/components/carousel/item as the @type to filter out events triggered by other components.

Next, push an event listener onto the data layer to listen for the cmp:show event.

window.adobeDataLayer.push(function (dl) {
     dl.addEventListener("cmp:show", teaserShownHandler);
});

The cmp:show event is triggered by many different components, like when a new slide is shown in the Carousel, or when a new tab is selected in the Tab component.

On the page, toggle the carousel slides and observe the console statements:

To stop listening for the cmp:show event, remove the event listener from the data layer

window.adobeDataLayer = window.adobeDataLayer || [];
window.adobeDataLayer.push(function(dl) {
    dl.removeEventListener("cmp:show", teaserShownHandler);
});

Return to the page and toggle the carousel slides. Observe that no more statements are logged and that the event is not being listened to.

Next, create an event handler that is called when page shown event is triggered:

function pageShownHandler(event) {
    var dataObject = getDataObjectHelper(event, {"@type": "wknd/components/page"});
    if(dataObject != null) {
        console.log("Page Shown: " + dataObject['dc:title']);
        console.log(dataObject);
    }
}

Notice that the resource type wknd/components/page is used to filter the event.

Next, push an event listener onto the data layer to listen for the cmp:show event, calling the pageShownHandler.

window.adobeDataLayer = window.adobeDataLayer || [];
window.adobeDataLayer.push(function (dl) {
     dl.addEventListener("cmp:show", pageShownHandler);
});

You should immediately see a console statement fired with the page data:

The cmp:show event for the page is triggered on each page load at the top of the page. You might ask, why did the event handler get triggered, when the page has clearly already been loaded?

One of the unique features of the ÃÛ¶¹ÊÓƵ Client Data Layer is you can register event listeners before or after the Data Layer has been initialized, it helps to avoid the race conditions.

The Data Layer maintains a queue array of all events that have occurred in sequence. The Data Layer by default will trigger event callbacks for events that occurred in the past and events in the future. It is possible to filter the events from past or future. .